One example of an increasingly more popular type of UE is a Machine Type Communications (MTC) device. MTC devices run applications generating data that is typically delay-tolerant and oftentimes lower priority traffic as compared to non-MTC UEs. Because MTC devices are and will continue to be deployed in very high numbers, overload situations are expected to become more common. FIG. 1 illustrates one example of a communication network including a core network node such as a serving gateway (S-GW) 14, a plurality of base stations 12 referred to in LTE as eNodeBs (eNBs), and a large number of UE devices 10 including many MTC devices. Access to the wireless communication network may, for example, be by way of a contention-based random access channel (RACH). Base stations (eNBs) 12 provide radio network access to and from the UEs 10, and in LTE, collectively form a radio access network (RAN). The S-GW 14 connects to an external packet data network (PDN) such as the Internet via a PDN Gateway (PDN GW) 16. The UEs 10 may communicate with one or more servers, including one or more MTC servers 18, connected to the S-GW 14 or to the PDN GW 16 as shown. The cloud represents a communications network such as the Internet.
Machine Type Communications (MTC) traffic is defined as a specific type of wireless communication network traffic in the 3rd Generation Partnership Project (3GPP) Technical Specification 23.888, “System Improvements for Machine-Type Communications,” the disclosure of which is incorporated herein by reference in its entirety. The term UE includes but is not limited to MTC devices that typically primarily collect and report data and/or non-MTC devices. One non-limiting example of an MTC device is a gas or power meter with a wireless transceiver for reporting at predetermined time periods, or event-based, the usage of gas or electrical power to the MTC server 18. Non-MTC devices are devices, such as a cell phone, smart phone, laptop computer, etc., used for voice and data communications by human users. While an MTC device may comprise a dedicated device specifically for data collection and reporting, a combined UE 10 may function part of the time as an MTC device and part of the time as a non-MTC device.
Both MTC devices and non-MTC devices all must contend with one another for access on the RACH. Due to the rapid growth of MTC devices, it is expected that the number of MTC devices will far exceed the number of non-MTC devices in the near future. Those large numbers will likely result in congestion, for example in the radio network, particularly when many of the MTC devices simultaneously try to access the network. Many such devices will likely transmit small amounts of uplink (UL) data (e.g., 100 bits) periodically (e.g., once per hour). For this type of data transfer, a network access procedure constitutes a significant part of the total signaling required to communicate the message. The time between each message is also typically long, and therefore, the UE may need to perform a new random access for each message it transmits, thereby degrading performance.
In LTE there are plans for enhanced MTC coverage with a target to improve the link budget, e.g., by approximately 20 dB as compared to what is supported with the legacy LTE standard. See 3GPP Technical document (Tdoc) RP-121441.
Networks seek to balance UE loads for both idle mode UEs and active mode UEs. For example, an idle mode UE may be instructed to camp on another network and an active mode UE may be instructed to perform an inter-Radio Access Technology (RAT) handover in an effort to reduce the current load in the currently-accessed network. But such load-balancing procedures may be insufficient. For example, even though UEs may be instructed to camp on a certain network and listen for paging messages from that network, there is no guarantee that the UE will use that same network when the UE needs to perform an UL network access.
UEs traditionally select a cell and a network based on UE measurements of base station/cell signals transmitted in the downlink (DL), which gives a good indication of the downlink quality that can be achieved in different cells and the networks that operate those cells. For MTC devices, it is often more relevant to select the network with the best uplink (UL) radio communications. For several reasons the UL and DL channel quality might be significantly different, and traditionally there has been no easy way for a particular UE to determine which network provides the best uplink (UL) radio communications. For example, different nodes may use different transmit power. Two signals reaching the UE with similar power might be transmitted with 20 dB difference in power or more. In this example situation, the uplink to one of the nodes (associated with the signal transmitted with weaker power) may also be 20 dB better or more. But the UE is unaware of this.
This problem is even more serious in a heterogeneous network deployment where low power base stations are in a sleep mode where they do not transmit any signals, even though they monitor random access channels in the uplink. Another example when the UE can not easily determine the UL quality is if one node has a much better receive antenna than another node. There might also be other subtle differences in base station receiver hardware, such as receiver circuitry noise sensitivity, that the UE can not take into consideration when performing network selection. In such cases, a stationary MTC device might consistently perform random access to an inappropriate network, or it may use inappropriate parameters when performing random access. If many MTC UEs behave in this fashion, then overall system performance will suffer.
Consider a case where a UE can use two different networks (e.g., a legacy LTE network as well as a separate network for enhanced MTC coverage). In that case, a network selection needs to be performed. But if the UE selects the wrong network, the overall system efficiency deteriorates, thereby making it more difficult for other UEs to access the network. And forcing the UE to perform a handover to the appropriate network creates undesired signaling and operations.
Even if the UE receives only one set of signals designed for enhanced MTC coverage, it might still be difficult for the UE to perform a proper network selection. Consider for example a heterogeneous network scenario where small indoor nodes are put into sleep mode during low traffic conditions. Here, the only signal reaching the UE may be the new signals designed for enhanced MTC coverage. But small indoor nodes may still be actively receiving in the uplink, in which case, a particular UE should not fall back to using the network defined for enhanced MTC coverage but should instead use the normal legacy network. But the UE is not aware of this because it can not detect the presence of the nearby sleeping low power indoor node.
The number of MTC device UEs is expected to be much larger than the number of non-MTC device UEs. If a very large number of such devices consistently perform network access selecting a less optimal network, then the system performance can be severely degraded. The UE should select the network with the best uplink performance, and to do so, it needs sufficient the information to make that selection. Another issue that relates to selecting the best network is load balancing between networks. If many MTCs decide on their own which network to use for communication, then the networks will have difficulty performing effective load-balancing amongst the networks.